Field of Invention
The present disclosure relates to an optical sensor, and more particularly, to an optical sensor including an external cavity laser.
Description of the Related Art
When a material desired to be detected is attached onto a grating, a wavelength of a peak of reflectance is changed according to a refractive index of the material, so that the grating may be utilized as a sensor based on the aforementioned phenomenon. An example of the grating utilized as the sensor includes a Guided Mode Resonance Grating (GMRG). The GMRG refers to a grating operated as a high efficient band stop filter at a resonant wavelength when a grating period on a plane wave guide satisfies a resonance condition generated by a combination of incident light and a period structure.
A sensing system, which implements an External Cavity Laser (ECL) using the GMRG and measuring and digitizing a change in a wavelength by a material attached to the GMRG has been suggested. The sensing system using the GMRG in the related art has a problem in that it is necessary to digitize a fine change in an oscillation wavelength by using a high resolution spectroscope.
Further, there is a case where the sensing system using the GMRG in the related art uses one semiconductor optical amplifier in order to measure a reference oscillation wavelength and a sensing oscillation wavelength at one time, and when a reference mode and an oscillation mode are close, only one mode is oscillated by a mode competition, so that it is impossible to measure the wavelength.